This invention relates to a low range splitter transmission, and specifically to a low range splitter transmission capable of shifting while the vehicle is in motion from a highest numerical gear ratio to a second highest numerical gear ratio.
Typically, a range splitter transmission for a heavy truck includes a main gearbox and an auxiliary gearbox. The auxiliary gearbox includes a plurality of selectable gears for expanding the number of available gear combinations. The main gearbox includes a plurality of gears selectable in combination with gears within the auxiliary gearbox.
Many configuration and variations of range splitter transmissions are available to provide an expanded selection of gear ratios. A known range splitter transmission utilizes the gears within the auxiliary gearbox to subdivide gear ratios available within the main gearbox. Another known type of range splitter transmission utilizes the gears with in the auxiliary gearbox in combination with those within the main gearbox to provide low speed high torque. Typically, low speed and high torque are required in heavy off road vehicles, such as construction and mining vehicles.
In some heavy vehicle applications, the highest numerical gear ratio available is much higher than the second highest numerical gear ratio. The highest numerical gear ratio is often referred to as Low Low or Low Split, and the second highest numerical gear ratio referred to as First gear or Low. The large numerical gear ratio step between the Low Low gear and First gear often is so extreme that the vehicle must be completely stopped in order to upshift from Low Low to First gear. As appreciated, in many instances it is not desirable or feasible to stop the vehicle to make the required gear change.
Currently available low range splitter transmission designs are based on a main gearbox that includes a single main gearbox gear used in concert with auxiliary gearbox gears. The highest numerical gear ratio within the main gearbox gear is typically used in combination with gears in the auxiliary gearbox for Low Low and First gears. Typically, the overall range between the highest and lowest numerical gear ratios provided by the transmission is fixed. The difference in ratios between the highest numerical gear ratio (lowest vehicle speed) and lowest numerical gear ratio (highest vehicle speed) must span a desired range in order to provide desired speeds for a specific application.
In order to cover the entire gear ratio range, a step or change in numerical gear ratio between each gear combination is determined and corresponding numerical gear ratios for each specific gear are selected. The span between the highest gear ratio and the lowest gear ratio results in wider or uneven ratio steps between gears. In order to obtain acceptable ratio increases between the most used gears, the gear ratio steps between the highest numerical gear ratio and the second highest numerical gear ratio is greater than would allow realistic shifting during movement of the vehicle.
Accordingly, it is desirable to design a range splitter transmission that spans a desired range of gear ratios while still providing gear ratio steps between speeds that allow shifting to occur while the vehicle is in motion.